Though I tend to give chain restaurants a hard time, they make for fascinating study. They are treasuries of fashion, fads and folklore, business case studies both inspiring and sobering, barometers of evolving popular tastes and changing demographics.

Regional differences alone could fill a book. Living on the East Coast, I saw Papa John's and Domino's delivery cars everywhere. Here they dart like feral kittens, trying to avoid big, bad Imo's. I'd never heard of Culver's or Sonic before I moved to the Midwest; when I have a hangover-induced fast-food craving, I wish in vain for a Roy Rogers. (Yes, as in the cowboy.)

Case in point: I had no idea Ba Le, the Vietnamese café and bakery that opened last fall on South Kingshighway between Arsenal and Chippewa, was once a Long John Silver's. I vaguely recall Long John Silver's from my childhood, but there weren't enough locations for its distinctive look to plant itself in my memory.

And I never would have guessed that Ba Le is an independently owned franchise of a national chain. The Ba Le chain was founded in San Jose, California, in 1982, according to the corporate Web site (www.balefranchisecorp.com), and it now has more than 30 locations spread across a dozen states.

Though Ba Le is a chain, it doesn't appear to have one standardized menu. In fact, the St. Louis location itself doesn't seem to have one standardized menu: There is a picture menu on the wall behind the counter, from which most of the customers I saw ordered. There is also a photocopied takeout menu, which more or less matches the menu on the wall. And there is a third, longer menu, which I didn't find until the woman taking my order handed it to a companion during my final visit.

Regardless of which menu you have, Ba Le's specialty is the banh mi. This was a fusion dish long before fusion became fashionable — and it remains one of the few positive consequences of France's colonial occupation of Vietnam. Quite simply, banh mi is a sandwich served on a baguette. Yet the beauty of banh mi is that very simplicity. Unlike most American sandwiches these days, which are overstuffed and sloppy with condiments, banh mi are neatly contained, a model of efficiency and balance. You get a thin layer of chopped or sliced meat topped by a combination of vegetables both pickled and fresh — usually carrot, radish, onion and jalapeño peppers — and a few sprigs of cilantro.

The key is the baguette. It needs to be crusty enough to support its contents — but not so crusty that it shreds your gums. The baguettes at Ba Le are very good, and I enjoyed each of the banh mi I tried. Most interesting was the one I discovered on my final visit, when the third menu appeared: red pork belly. The luscious, thinly sliced meat seemed to melt like butter into the bread. The meat in the other banh mi I tried — grilled pork, barbecue pork and roasted chicken — wasn't quite as distinctive, though that was more on account of the fresh, sharp flavors of the vegetables, especially the (unseeded) jalapeños.

I also tried orders of spring and summer rolls. You get three very plump rolls to an order, almost enough to be a full meal. The spring rolls boasted shrimp and thinly sliced pork, but fresh basil was the most prominent flavor. Summer rolls featured slices of dense, smoky sausage and a bracing mint bite.

Ba Le also serves baked goods. I had a pastry that looked something like a hollowed-out croissant with a thin, sweet strawberry jelly. Not bad, though not as flaky as I prefer. You can also get soup, rice and vermicelli dishes, and even pork pâté or head cheese to go. Just about everything I had cost less than $5 — and at $2.50 to $3.50 apiece, the sandwiches are practically a steal.

Just inside the entrance to Cheeburger Cheeburger is a bulletin board with snapshots of those hardy souls able to finish "The Full Pounder." This, in fact, has a weight of twenty ounces before it is cooked. Once you add bun, toppings and condiments, I suspect it tops a pound again.

Cheeburger Cheeburger opened at the Westfield Chesterfield shopping mall only a few months ago. The bulletin board is already full.

Not too surprising. As you'd hope at a place named Cheeburger Cheeburger, the burgers are decent. You choose a weight (five choices, from a bit more than a quarter of a pound to "The Full Pounder"), a cheese and as many toppings as you want from a lengthy list that offers the basics as well as pepperoni, onion rings and Old Bay seasoning. (Bacon, sautéed onions and sautéed mushrooms are extra.)

On my first visit, I had the half-pound burger (a.k.a. "The Serious"), medium, with cheddar, bacon, lettuce and tomato. A soft but sturdy bun, crisp bacon and passably fresh toppings made for a fine meal. When I returned I tried the patty melt (also half a pound), which is served with Swiss and sautéed onions.

It was this second burger that revealed my only real complaint with these burgers. Cheeburger Cheeburger uses ground Black Angus beef. This is fine — better than fine, considering most places won't tell you what kind of beef you're getting, let alone give you good beef. That said, it's a shame you can't order burgers cooked medium-rare at Cheeburger Cheeburger, because a little more beefy, bloody flavor would have taken these up a notch. The rye bread on which the patty melt was served was so strongly flavored that the burger had a hard time competing with it.

Cheeburger Cheeburger boasts more than 60 locations in 18 states. At first glance it seems like one of those chains we restaurant critics can't wait to savage. It's a faux diner, with shakes and egg creams and oldies playing on the speakers. Worse, it's a faux diner that "borrows" the famous Saturday Night Live "Cheezborger Cheezborger" shtick. (A sign on the wall even bears the "No Coke, Pepsi" punch line.)

In fact, when Cheeburger Cheeburger attempted to expand into the Chicago area, the restaurant that inspired the SNL skit sued. The tiff was soon settled: Cheeburger Cheeburger kept its name, but it can't open anywhere near Chicago. (Cheeburger Cheeburger obviously values this name highly. The brand is everywhere: T-shirts for sale, signs on the wall, a bag of its proprietary onion-ring batter on every table.)

Despite the branding, Cheeburger Cheeburger doesn't overdo the diner motif — and the help stays away from turning the place into a comedy routine. When I ordered Coke, the waiter gamely asked if Pepsi was OK. Aside from salads and a few chicken sandwiches, the restaurant sticks to what it does best: burgers, fries and onion rings. The fries are freshly cut and served a crisp, coppery brown. The onion rings are excellent, thinly sliced and lightly battered. The only disappointment was the much-too-thin dreamsicle shake I tried.

Make that two disappointments. Near the bulletin board honoring those who vanquished "The Full Pounder" is a board celebrating kids twelve and under who were able to eat a half-pound burger. Here we find chains — and American dining in general — at their worst: celebrating the supersized, encouraging kids to gorge.

The good news is that, when I visited, there were far fewer pictures of kids than of adults.

The bad news is that the kids' bulletin board already had a section set aside for "Repeat Offenders."